This study examined the performance and photo-bias stability of double-channel ZnSnO/InZnO (ZTO/IZO) thin-film transistors. The field-effect mobility (μFE) and photo-bias stability of the double-channel device were improved by increasing the thickness of the front IZO film (tint) compared to the single-ZTO-channel device. A high-mobility (approximately 32.3 cm2/Vs) ZTO/IZO transistor with excellent photo-bias stability was obtained from Sn doping of the front IZO layer. First-principles calculations revealed an increase in the formation energy of O vacancy defects in the Sn-doped IZO layer compared to the IZO layer. This observation suggests that the superior photo-bias stability of the double-channel device is due to the effect of Sn doping during thermal annealing. However, these improvements were observed only when tint was less than the critical thickness. The rationale for this observation is also discussed based on the oxygen vacancy defect model.

Recently, amorphous metal-oxide thin-film transistors (TFTs) have attracted considerable interest as attractive backplane electronics for active matrix organic lightemitting diodes (AMOLEDs) and transparent displays because they offer high mobility, low-temperature processability and good transparency to visible light [1,2]. In particular, low power consumption is one of the key issues for the mobile applications, such as smart phones and tablet personal computers, due to the limited capacity of the rechargeable lithium-ion battery used as power source [3]. The use of a high-k dielectric film as a gate insulator is an effective approach for enhancing the capacitive coupling and reducing the power consumption. Many studies have examined the adoption of high-k dielectric materials, such as HfO 2 [4], TiO 2 [5], AlTiO [6], Ta 2 O 5 [7,8], HfLaO [9] and ZrO 2 [10] in the transition-metal-oxide TFTs. These have generally been fabricated by vacuum deposition methods, such as pulsed laser deposition (PLD) [4], atomic layer deposition (ALD) [5,6], evaporation [7-9] and sputtering [8,10], which require expensive vacuum equipment. In contrast, solution-based deposition techniques, such as spin coating would offer a range of merits, such as simplicity, low cost and high throughput. In this regard, very re-cently there have been many reports on the soluble processed high-k gate dielectrics such as ZrO 2 [11][12][13], Y 2 O 3 [14,15] and HfO 2 [16] for metal-oxide TFTs. Among these high-k dielectrics, the ZrO 2 material is promising due to its high relative permittivity, wide bandgap (5-8 eV) and good thermal stability [17]. Lee et al. reported the highmobility (27.3 cm 2 /V s) ZTO TFTs with soluble processed ZrO 2 gate insulator at an annealing temperature of 500 °C [13]. However, the annealing-temperature-dependent structural property and the resulting electrical performance was not examined in detail. In this Letter, we investigated the effect of annealing temperature on the soluble processed ZrO 2 gated indium zinc oxide (IZO) TFTs. It was found that the low-voltage, high-mobility IZO TFTs with soluble processed ZrO 2 gate insulator can be fabricated at an annealing temperature of 400 °C.A heavily doped p-type silicon (p ++ Si) wafer was used as the bottom gate electrode. A precursor solution for the ZrO 2 film was synthesized using a sol-gel process with ZrCl 4 , HNO 3 and H 2 O dissolved in ethanol. The concentration of the metal precursor was 0.5 M and the ratio of ZrCl 4 :HNO 3 :H 2 O was 1:10 :10. The solution was spincoated on a bare Si substrate for 30 s at 5000 rpm. The re-Spin-coated zirconium oxide films were used as a gate dielectric for low-voltage, high performance indium zinc oxide (IZO) thin-film transistors (TFTs). The ZrO 2 films annealed at 400 °C showed a low gate leakage current density of 2 × 10 -8 A/cm 2 at an electric field of 2 MV/cm. This was attributed to the low impurity content and high crystalline quality. Therefore, the IZO TFTs with a soluble ZrO 2 gate insula-tor exhibited a high field ef...

Transition tantalum induced crystallization of amorphous zinc tin oxide (a-ZTO) was observed at low temperature annealing of 300 °C. Thin-film transistors (TFTs) with an a-ZTO channel layer exhibited a reasonable field-effect mobility of 12.4 cm2/V s, subthreshold swing (SS) of 0.39 V/decade, threshold voltage (VTH) of 1.5 V, and ION/OFF ratio of ∼107. A significant improvement in the field-effect mobility (up to ∼33.5 cm2/V s) was achieved for crystallized ZTO TFTs: this improvement was accomplished without compromising the SS, VTH, or ION/OFF ratio due to the presence of a highly ordered microstructure.

This paper examined the effects of postdeposition annealing on the electrical properties of titanium-capped (TC) indium-zinc oxide (IZO) films and their IZO thin-film transistors. The TC IZO transistor oxidized at the temperature of 300°C exhibited a high field-effect mobility of 61.0 cm 2 /Vs, low subthreshold gate swing of 110 mV/decade, V th of −0.4 V, and high I ON/OFF ratio of 2.3 × 10 8 . In addition, the positive gate bias stress-induced stability of the TC IZO transistor was better than that of the control device without metal capping treatment. This was attributed to the scavenging effect of the loosely bonded oxygen species in the IZO semiconductor by titanium thermal oxidation.Index Terms-Indium zinc oxide (IZO), metal capping, mobility, oxygen-related defect, thin-film transistors (TFTs).

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